Automatic emergency drain for floating tank roof



J. H- WIGGINS Oct. 8, 1957 AUTOMATIC EMERGENCY DRAIN FOR FLOATING TANK ROOF Filed Aug. 16, 1956 nvmvrozz. J5 ZZ/ United States Patent 2,808,958 Patented Oct. 8, 1957 AUTOMATIC EMERGENCY DRAIN FOR FLOATING TANK ROOF John H. Wiggins, Menlo Park, Calif.

Application August 16, 1956, Serial No. 604,536

8 Claims. (Cl. 220-26) This invention relates to improvements in field storage tanks of the floating roof type, and more particularly to an improved automatic safety drain structure for draining precipitation from a floating type tank roof when the tank is substantially empty and the roof is supported upon the bottom portion of the tank.

In the construction of large floating roofs for field storage tanks for oil and the like, it is common practice to provide the underside of such a roof with a plurality of downwardly extending legs upon which the roof is adapted to rest at the bottom of the tank when the tank is empty. These legs ordinarily support the roof some two or three feet above the floor of the tank, thereby providing a crawl space under the roof that will permit convenient inspection and maintenance of both the underside of the roof and the bottom of the tank. These sup porting legs are very desirable, but they give rise to a safety problem with respect to precipitation that may collect upon the roof while the tank is empty and while the roof is resting upon the legs. Although a floating type roof may be designed to carry a load of as much as 8 inches of accumulated rainfall while the roof is in a floating condition and buoyantly supported throughout its area by the liquid in the tank, an accumulation of a much lesser amount of water on the roof while the roof is resting on the supporting legs may overstress the roof structure and cause severe damage thereto.

Heretofore, the builders of tanks of the floating roof type have sought to avoid accumulation of excessive precipitation on the roofs by providing each roof with a hose or drain pipe that leads from a low point on the roof, downwardly through the oil in the tank and outwardly through. the wall of the tank adjacent its bottom. These drains have ordinarily been quite adequate when they were open, but in order to avoid the danger of losing oil from the tank in the event a leak should occur in the drain system within the tank, the drain pipes have been provided with manually operated valves that are ordinarily maintained in a closed condition. In most such installations a manually operated valve has been provided in the drain system exteriorly of the tank adjacent its base, and in some installations a manually operated valve has also been employed on the roof so as to prevent oil from flowing onto the top of the roof inthe event a leak should occur in the drain pipe while the roof is floating. In any event, when a heavy rainfall has begun or has been exproviding a simple, inexpensive, fool-proof, emergency drain structure for floating-type tank roofs that is automatically prepared, in response to the settlingof the roof to the bottom of the tank, to drain excessive accumulations of precipitation therefrom. Another object of the invention is to provide a drain structure of the character just mentioned that i automatically conditioned, in response to flotation of the roof, to insure against any flow of liquid from the interior of the tank through the drain structure and onto the upper side of the roof even though the roof may become abnormally loaded by precipitation or other weights during flotation. Yet another object of the invention is to provide a drain passageway from the upper side or" the roof to the interior of the tank, wherein the upper end of this passageway is automatically elevated with respect to the roof when the roof is in a floating condition, so as to prevent flow of liquid from the interior of the tank onto the upper side of the roof through the passageway, and wherein the upper end of the passageway is automatically lowered to a position adjacent the deck of the roof in response to settling of the roof to the bottom of the tank, thereby permitting precipitation that may fall upon the deck to be drained through the passageway and into the interior of the tank. Still another object of the invention is to provide in said passageway a one-Way valve that further insures against flow of liquid from the interior of the tank through the passageway and onto the upper side of the deck. Another object of the invention is to arrange said one-way valve in said passageway in such a manner that it will ordinarily not be contacted by liquid from Within the tank, thereby avoiding fouling of the valve. Yet another object of the invention is to provide means for maintaining in said passageway a water leg that seals the passageway against fumes from the interior of the tank and also tends to avoid contact between said one-Way valve and the liquid from the interior of the tank.

These and other objects and advantages of the present invention will be apparent from the following description of a preferred form of the invention, and a modification thereof, taken with the accompanying drawing, wherein:

Fig. 1 is a vertical cross-sectional view taken through a tank having a floating-type roof provided with an emergency drain structure in accordance with the present invention, the roof being shown in full lines in its floating condition and being shown by broken lines in the posipected, it has heretofore been necessary for personnel to go about opening the valves of the drain systems of tion it occupies when the tank is empty and when the roof is resting upon supporting legs on the bottom of the tank.

Fig. 2 is an enlarged cross-sectional view showing the drain structure of the present invention; and

Fig. 3 is a similar view showing a modified form of the structure.

In. the drawing the numeral 10 designates, generally. an upright cylindrical tank having upstanding side walls 11 and a bottom 12 that may be slightly crowned at its center and which may rest upon'the ground 13 or upon any suitable supporting base. Tanks of this general type are well known' and they find wide use for the storage of liquid petroleum products and liquids of other kinds. The tank is provided, in the present instance, with a floating roof of the peripheral pontoon type. This roof comprises a circular deck 14 that may be constructed by the welding or riveting together of suitably shaped plates. The peripheral portion of the deck is provided with an upstanding rim 15 and with an upstanding outer rim 16 concentrically arranged and spaced radially outwardly with respect to the rim 15, the peripheral lim l5 and the rim 16 being joined across their upper and lower edges by substantially horizontal annular plates 17 and 17' so as to provide a circular pontoon about the periphcry of the roof. The space between the outer surface of the peripheral rim 16 and the inner surface of the upstanding wall 11 ofthe tank may be closed by a seal of any well known construction, and the entire roofis adapted to float upon the liquid contents of the tank, with the entire under-surface of the deck 14 buoyantly supported by the liquid so that the roof will rise and fall with variations in the liquid level.

In order to provide a support for the roof when the tank is empty, the underside of the deck 14 is provided with a plurality of downwardly extending legs 18 adapted to come to rest upon the bottom 12 of the tank when the liquid has been drained from the tank, the legs being arranged to support the entire root somewhat above the bottom 12 of the tank so as to leave a space under the roof in which workmen may carry out any repairs or maintenance that may be necessary from time to time both on the bottom of the tank and on the underside of the roof.

The deck 14 of the roof is provided with a slight pitch so that precipitation that may fall upon the roof from time to time will drain toward its center. At the center of the roof there is provided a recessed cup 19 which will tend to receive the precipitation and cause the same to be introduced into a flexible drain tube 20 which extends in the usual manner downwardly into the interior of the tank and laterally through the wall 11 thereof, where the tube joins with an external drain conduit that is provided with a valve 22. The cup 19 and the tube 20, as previously suggested herein, comprises a well-known drain construction widely used -for disposing of precipitation that may collect upon the top of the roof. However, due to the fact that a leak occurring in the tube 20 will permit the liquid contents of the tank to drain into the external drain conduit 21, the valve 22 is normally kept shut and is manually opened only when it becomes obvious that drainage of the roof will shortly be necessary or when a substantial amount of precipitation has already been collected upon the roof. When the roof is in a floating condition upon the liquid in the tank, the accumulation of large amounts of water upon the deck 14 of the roof will ordinarily cause no damage to the roof due to the fact that the deck 14, throughout its entire area, is buoyantly supported by the liquid within the tank. This, however, is not the case when the roof is resting upon the spaced apart legs 18 upon the bottom 12 of the tank. Thus, it will be appreciated that if the maintenance personnel in charge of the tank should fail to open the valve 22 when the roof is resting upon the bottom of the tank, precipitation may be collected upon the roof in sufiiciently excessive amounts to overstress and to bend the several plates comprising the deck 14 of the roof.

In order to avoid the danger of the inadvertent collection of excessive amounts of precipitation upon the deck 14 of the roof when the roof is resting upon the legs 18, there is provided an automatic emergency drain, of the character illustrated in detail in Figs. 2 and 3, adjacent the low point of the roof. Referring specifically to Fig. 2, it will be seen that this drain comprises a conduit 23 which extends downwardly through the deck 14, with the lower end of the conduit opening into the interior of the tank beneath the roof. The conduit at the point at which it passes through the deck 14 is welded to the deck, as at 24, in order to make a liquid-tight joint, this being desirable since the deck 14, and particularly its low point, is located somewhat below the level of the liquid in the tank when the roof is in a floating condition. The upper end of the conduit comprises an elbow 25 having a laterally extending leg 26 to which there is joined a flexible tube 27, or the like, having a free end adapted for vertical movements with respect to the deck 14. The tube 27 may be joined to the leg 26 of the elbow 25 in any suitable liquid-tight manner and, if desired, the interior of the leg 26 of the elbow may be provided with a one-way valve that is shown schematically at 28, which will permit the flow oi liquid, through the tube 27 and downwardly through the. conduit 23 only in the direction of the arrows. 29 and 30.

The outer or free end of the tube 27 has a clamp ring 31 secured thereabout having an eye piece 32 to which the lower end of a rod, chain or cable 33 is secured, the other end of the element 33 being pivotally secured to the outer end portion 34a of a lever 34 that is pivotally mounted at 35 upon a bracket 36 extending diagonally upwardly from the external wall of an upstanding hollow pipe 37 that is welded at its base upon the deck 14. The opposite end of the lever 34 has a counter-weight 38 suspended therefrom so that the lever 34, in its normal condition, will be. pivoted in a counter-clockwise direction by the counter-weight to the position shown by the broken lines in Fig, 2, thereby lifting the free end of the tube 27 well above the deck 14 and well above the level that the liquid in the tank will occupy with respect to the roof when the roof is in a floating condition. An opening 39 is provided in the deck 14 within the base of the upstanding pipe 37 and a vertical rod 40 extends downwardly through the pipe 3.7 and through the opening 39 in the deck, the upper end of this rod being pivotally secured at 41 to the lever 34, as shown in Fig. 2.

When the roof is in a floating condition upon the liquid contents in the tank, the lever 34, being acted upon by the weight of the rod 40 and by the counter-weight 38, holds the free end of the tube 27 in its elevated position, thereby insuring against the possibility that liquid from within the tank may flow upwardly through the conduit 23 and through the flexible tube 27 onto the upper surface of the deck in the event the valve 28 should leak when the deck is subjected to an unusual load such, for example, as accumulated precipitation or the like, which may cause the liquid level within the tank to rise relative to the roof from a normal liquid level (designated by the line 42) to a high level (represented by the line 43). However, when the tank is drained and when the roof settles downwardly onto the bottom 12 of the tank, the lowermost end 40a of the rod 40 comes into contact with the bottom 12 of the tank prior to the engagement of the legs 18 therewith, thereby causing the rod 40 to be raised with respect to the roofto pivot the lever 34 in a clockwise direction (as viewed in Fig. 2) to lower the flexible tube 27 to its full line position illustrated in Fig. 2. This automatic lowering of the tube 27 in response to the settling of the roof toward the bottom 12, positions the tube so that accumulation of precipitation not drained from the roof by the normal drain tube 20 will flow through the flexible tube 27 and downwardly through the conduit 23 into the interior of the tank, where the precipitation will be accumulated in a sump 44 and be drained therefrom through a suitable waste conduit 45. When oil or the like is again introduced into the tank, and when the supply of the oil becomes sufficient to float the roof and its legs 18 01f of the bottom of the tank, the roof and its deck 14 will begin to rise, thereby permitting the counter-weight 38. and the weight of the downwardly extending rod 40 to pivot the lever 34 in the counter-clockwise direction to raise the flexible tube 27 and thereby deactivate the emergency drain system.

In conjunction with this lifting. of the free end of the flexible tube 27, it will be noted in the embodiment of the invention shown in Fig. 2 that, inasmuch as the distance between the pivot points 35 and 41 is much less than the distance between the pivot point 35 and the outer end 34a of the lever 34, the rate at which the free end of the tube 27 will be raised with respect to the roof deck 14 during the initial floating movement of the roof will greatly exceed the rate at which the deck 14 is raised by the rising liquid within the tank. This insures that the free end of the tube 27 will be well elevated before the level of the liquid within the tank is increased to such an extent that some of the liquid might flow upwardly through the conduit 23 and out of the tube 27 onto the top of the deck in the event the deck is bearing an unusual load and in the event the one-way valve 28 leaks or is not employed in the system.

The elbow 25 is preferably disposed on the upper end of the conduit 23 somewhat above the deck 14 so that the one-way valve 28 within the leg 26 of the elbow will normally be located slightly above the normal relative level of the liquid within the tank, this normal relative level being represented by the broken line 42 in Fig. 2. This tends to prevent the liquid within the tank from coming into contact with the valve 23 and fouling the same. As an added measure of safety when the tank is used for the storage of oil or other petroleum products, provision may be made for keeping the conduit 23 full of water, thereby preventing the escape of fumes from the liquid in the tank through the conduit and also avoiding contact between the one-way valve 28 and liquid from the interior of the tank. In this connection, the lowermost end of the conduit 23 may be provided with a plurality of brackets 46 which support a Water cup 47 in a position such that the upper edge of the cup is located well above the lower opening of the conduit 23 contained within the cup. The elbow 25 may have an upstanding pipe 48 extending upwardly therefrom, with a funnel-shaped rain catcher 49 secured upon its upper end. At the same that the roof is being initially floated by the introduction of liquid into the tank, water can be poured into the rain catcher so that the conduit 23 is gradually filled with water as the liquid level within the tank rises. The amount of water that will be retained within the conduit 23 in a standing column will, of course, depend upon the length of the conduit and the specific gravity of the liquid within the tank but, by virtue of the cup 47, suificient water will be contained within the conduit 23 to seal the same and, under normal circumstances, to prevent the liquid within the tank from coming into contact with the valve 28 in the elbow 25'. The supply of water within the conduit 23 will, of course, be replenished from time to time as precipitation is caught by the rain catcher 49 and funneled downwardly through the pipe 48 into the conduit 23. Any water that overflows from the cup 47 will drop downwardly through the oil in the tank and be collected in the sump 44.

It will be appreciated that various means other than the pivoted lever 34 may be employed for automatically raising and lowering the free end of the flexible tube 27 in response to movement of the tank roof with respect to the bottom 12 of the tank. One such alternate means is illustratedin Fig. 3. In this modification a cable is secured to theeye piece 32 of the clamp ring 31 at the free end of the flexible tube 27 and this cable is arranged to be wrapped upon a drum 51 secured upon one end of a shaft 52 that is suitably journalled upon a bracket 53 fastened to the exterior wall of the upstanding pipe 37. The other end of the shaft 52 has a small pinion 54 thereon which meshes with a toothed rack 55 formed upon the upper end portion of the downwardly extending rod 40. The opposite sides of this rack may be provided with stop members 56 arranged to engage the upper end of the upstanding pipe 37 to limit the downward movement of the rod 40 with respect to the roof. The combined weight of the rod 40 and the rack 55 is suflicient to cause the rod and rack to move downwardly with respect to the roof as the rising liquid within the tank begins to float and lift the roof off the bottom 12 of the tank. This relative downward motion of the rod 4th and the rack 55 will rotate the pinion 54 and thus cause the drum 51 to wind the cable 40 thereon to raise the free end of the flexible tube 27 when the roof is floated ofl the bottom of the tank. Conversely, as the roof is lowered onto the bottom 12 of the tank, the lowermost end 45a of the rod will come into contact with the bottom 12 of the tank before the legs 18 of the roof make contact therewith, thereby causing the rod and rack 55 to be moved upwardly with respect to the roof, causing the drum 51 to turn in a direction lowering the free end of the flexible tube 27 to the position thereof shown by the solid lines in Fig. 3, in which position excessive precipitation that may thereafter tend to accumulate upon the deck 14 of the roof will flow through the tube 27 and thence downwardly through the conduit 23 into the interior of the roof. when the ratio of the diameter of the drum 51 to the diameter of the pinion 54 is relatively great, as shown in Fig. 3, the rate at which the free end of the tube 27 will be raised with respect to'the deck 14, as the roof is floated off of the bottomof the tank, will exceed the rate at which the roof is raised with respect to the bottom of the tank. As previously explained in connectionwith the specific structure shown in Fig. 2, this insures that the free end of the tube will always be located above the liquid level in the tank, even when flotation of the roof is begun at a time when the roof is heavily loaded.

From the foregoing description it will be appreciated that the emergency drain structure of the present invention is extremely simple and inexpensive to construct, and that it provides an ideal means by which the accumulation of excessive amounts of precipitation upon a floating-type tank roof can be automatically avoided while the roof is resting upon the bottom of the tank. At the same time, it will be appreciated that the present invention provides all of the safety features that could be desired with respect to insuring against leakage of liquid from within the tank onto the top of the roof.

The present description has been given for purposes of better understanding only, and no unnecessary limitations should be understood to be intended thereby, for it will be understood by those skilled in the art that various modi fications may be made in the apparatus without departing from the spirit and scope of the appended claims. For example, in the present drawing only apparatus of a purely mechanical nature has been illustrated inasmuch as it representsthe simplest form of the present invention and presents no safety hazards when the invention is utilized in connection with tanks that are to contain inflammable products. It will readily be appreciated by those skilled in the art, however, that when safety will permit, various apparatus, including electrically actuated means, may be substituted forcertain of the purely mechanical elements illustrated in the present drawing, all within the scope of the appended claims.

I claim:

1. In combination with a tank roof of the type adapted to float upon liquid contained in the tank and to rise and fall as variations occur in the liquid level, a drain for disposing of precipitation that may collect upon the upper surface of the deck of the roof and may tend to overstress the roof structure when the tank is substantially empty and the roof is resting upon the bottom portion of said tank, comprising a drain conduit extending through said roof deck in liquid-tight fashion, with the lower end of said conduit opening into the interior of said tank beneath said deck, a tube on the upper side of said deck, said tube being joined at one of its ends to said conduit and having its other end free for vertical movements with respect to said roof deck, means connected to said tube for normally retaining said free end thereof in a well elevated position with respect to said deck to prevent the liquid in the tank from flowing onto the upper surface of the deck through said conduit and through said tube when said roof is floating upon said liquid, and means responsive to the settling of said roof into resting position upon said bottom portion of said tank for automatically lowering said free end of said tube from said elevated position to a position adjacent the upper surface of said deck, said tube and said conduit being so constructed and arranged that said lowering of said free end of said tube causes said tube and said conduit to provide a drain passageway through which precipitation may flow by gravity from the upper side of said deck into the interior of said tank to prevent accumulation of excessive amounts of precipitation upon said deck.

2'. The combination set; forth. in claim 1., inc uding a check valve in said ass geway arranged to prevent: the liquid, in the tank from flowing through said conduit and through said tube onto the upper surface of said deck when the level of said liquid is, above the level of said deck.

3. The combination set forth in claim 2, wherein said check valve is arranged in said, conduit and is disposed at a level above the normal level of said liquid relative to said deck.

4. The combination set forth in claim 2, wherein said check valve is arranged in said conduit; above said, deck and at a level above the normal level of said, liquid relative to said deck.

5. In combination with a tank roof of the type adapted o float. upon liquid cont ined in. the tank: and to rise, and fall as variations occur in the liquid level, a drain for disposing of precipitation that. may collect upon the upper surface of the deck of the roof and may tend to overstress the. roof structure when the tank is substantially empty and the roof is resting upon the 'bottom portion of said tank, comprising a drain conduit extending through said roof deck in liquid-tight fashion, with the lower end of said conduit opening into the interior oi said tank beneath said deck, a tube on the, upper side of said deck, said tube being joined at one of its ends to said conduit and having its other end free for vertical movements with respect to said roof deck, means connected to said tube for normally retaining said free end thereof in a well elevated position with respect, to said deck to prevent the liquid in the tank from flowing onto the upper surface of the deck through said conduit and through said tube when said roof is floating upon said liquid, means for maintaining a column of water in said conduit so as to prevent the escape of fumes from the interior of said tank through said conduit and said tube, and means responsive to the settling of said roof into resting position upon said bottom portion of said tank for automatically lowering said free end of said tube from said elevated position to a position adjacent the upper surface of said deck, said tube and said conduit being so constructed and arranged that said lowering of said free end of said tube causes said tube and said conduit to provide a drain passageway through which precipitation may flow by gravity from the upper side of said deck into the interior of said tank to prevent accumulation of excessive amounts of precipitation upon said deck.

6. The combination set, forth in claim 5', wherein said water column maintaining means includes a rain catcher connected to said conduit for directing precipitation into said conduit from time to time to replenish said column.

7. In combination with a tank roof of the type adapted to float upon liquid contained in the tank, and to rise and fall as variations occur in the liquid level, a drain for disposing of precipitation that may collect upon, the upper surface of the deck of the roof and may tend to overstress the roof structure when the tank is substantially empty and the roof is resting upon the bottom portion of said tank, comprising a drain conduit extending through said roof deck in liquid-tight fashion, with the lower end of said conduit opening into the interior of said tank beneath said deck, a tube on the upper side of said deck, said tube being joined at one of its ends to said conduit and having its other end free for vertical movements with respect to said roof deck, a counterweighted lever connected to said tube for normally retaining said free end thereof in a well elevated position with respect to said deck to prevent the liquid in the tank from flowing onto the upper surface of the deck through said tube and, said conduit, and a rod extending downwardly through an opening in said deck and arranged to engage the bottom of the tank when said roof settles to a position adjacent said bottom for automatically pivoting said lever to lower said free end of said tube from said elevated position to a position adjacent the upper surface of said deck, said tube and said conduit being so constructed and, arranged that said lowering of said free end of said tube causes said tube and said conduit to provide a drain passageway through which precipitation may flow by gravity from the upper side of said deck into, the interior of said tank to prevent accumulation of excessive amounts of precipitation upon said deck.

8. The combination set forth in claim 7, including a stand-pipe on the upper side of said deck encompassing said opening and said rod for receiving any liquid that may pass upwardly through said opening from the interior of said tank.

References Cited in the file of this patent UNITED STATES PATENTS 1,801,172 Patterson Apr. 14, 1931 1,990,627 Wiggins Feb. 12, 1935, 2,563,017 Feild Aug. 7, 1951 

